I guess it's because we are not living alone. Whatever we do, we are not alone.
If you need food, you need to get it from others - restaurant, market, etc.
If you need clothes, you need to get it from others - boutique, shop, etc.
If you need accomodation, you need to get it from others - rental place, developer, etc.
If you are working, you need to deal with colleagues, clients, etc.
If you are studying, you need to deal with friends, teachers, etc.
If you are holidaying, you need to deal with strangers, co-travellers, etc.
But I would like to stress that, when you care for others, do not expect anything in return.
Caring supposed to be something that you give to others in your own accord.
If there's no reciprocate on your caring and you don't like it that way, then just stop it. Don't start to get fumed up by the inconsiderate of others and blame others for not returning your kindness or caring. Just go and find one that you appreciate your caring. Why make yourself and others suffer?
Of course, caring supposed to be something that is to give and take. When you receive caring from others, you are supposed to return the kindness. This is the right attitude.
But what about when you received caring/kindness from one that you would not like to?
Who's the one that's having attitude problem now?